Transparent antenna

ABSTRACT

A transparent antenna includes a conductive material disposed on a surface of a non-opaque substrate in one or more conductive regions, wherein a geometry of the conductive regions defines an antenna pattern. A non-conductive material is disposed on the surface of the substrate in a fill pattern which is an inverse of the antenna pattern. An average optical transparency in the conductive regions and the non-conductive regions is at least 50%, and the average optical transparency in the conductive regions differs from that of the non-conductive regions by no more than 10%.

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned, co-pending U.S. patentapplication Ser. No. ______ (Docket K002201), entitled “Method forfabricating a transparent antenna,” by T. Tombs, which is incorporatedherein by reference.

FIELD OF THE INVENTION

This invention pertains to the field of antennas, and more particularlyto antennas on a transparent surface that are visually undetectable to ahuman observer.

BACKGROUND OF THE INVENTION

Mast or whip antennas mounted on the exterior of a vehicle such as anautomobile have been used for receiving and transmitting electromagneticsignals (e.g., radio waves). It is also possible to place embedded wireantennas of quarter or half wavelength in laminated rear windows ofvehicles. Such wires are easily visible and are therefore prohibited foruse in the front windshield or side windows of an automobile.

The use of thin-film antennas has been gaining popularity in recentyears. Thin-film antennas are generally formed by applying a thin layerof conductive material to sheets of plastic film such as polyester, andthen patterning the resulting sheets to form the conductive surfaces ofantennas. Alternatively, conductive material may also be deposited onplastic or other dielectric sheets in desired patterns to form theantennas with the use of well-known masking and deposition techniques.

One area where there has been increased interest in using such thin-filmantennas is for window-mounted applications in motor vehicles, aircraft,and the like. Due to the increasing need for different modes ofwire-less communication, thin-film window antennas represent a desirablealternative to populating a vehicle or aircraft structure with mastantennas, or other types of non-conformal type antennas, which candetract from the aerodynamic and aesthetic appearance of the surface.

Thin film antennas designed to be affixed to any window of the vehicle(e.g., the windshield) are known in the art. An example of such anantenna is described in U.S. Pat. No. 5,083,135 to Nagy et al., entitled“Transparent film antenna for a vehicle window.” Nagy et al. discloseusing a transparent conductive film, such as indium-tin-oxide (ITO), forthe antenna conductor. However, they acknowledge that there is acompromise between transparency, which requires a very thin layer ofITO, and sufficient film conductivity to give good antenna performance,which requires a thick layer of ITO. Nagy et al. attempt to solve thisproblem by placing the antenna very high up on the windshield toinductively couple it to the car body. This substantially restrictsdesign freedom.

There is a conflict between the optical transparency and theconductivity (or surface resistance) of thin-films utilized to make suchantennas. For example, copper films having a surface resistance of about0.25 milliohms/square are commercially available, but their transparencyis well below the desired level of 70%. Other commercially availablethin-films formed from conductive materials such as ITO or silver haveacceptable transparencies (for example, AgHT™ silver type films haveoptical transparencies greater than 75%), but such films have surfaceresistances in the range of 4-8 ohms/square, which is several orders ofmagnitude greater than that of the above copper films, or conventionalconductors used for antenna construction. When transparent thin-filmshaving a higher surface resistance are used as the conductive surfacesfor an antenna, the performance of the antenna is substantiallydiminished. Antenna efficiency is reduced due to ohmic loss in thehigher resistance films, and as a result, antenna gain can be reduced byas much as 3-6 dB, depending upon the type of antenna.

The transparency of window-mounted thin-film antennas is an importantconsideration, but other factors are important to meet the requirementof invisibility. U.S. Pat. No. 7,656,357 to Ishibashi et al., entitled“Transparent antenna for vehicle and vehicle glass with antenna,”describes a transparent antenna to be installed on a glass surface of avehicle. Ishibashi et al. achieve good antenna performance and lighttransmittance using a copper foil with a low-reflection treatment andphotoetching to remove copper resulting in a sparse mesh pattern. Tofurther reduce the visibility of the mesh, Ishibashi et al. require agradation region of progressive wider openings and sparser lines in themesh pattern at the outlines of each mesh. U.S. Pat. No. 9,231,213 toSong et al., entitled “Methods for integrating and forming opticallytransparent devices on surfaces,” describes coplanar waveguide antennaswhere the edges of the mesh are critical to the radiation emitted andneed to be the highest conductivity region in the mesh and should not becompromised to reduce visibility.

In the past, attempts have been made to improve the efficiency oftransparent thin-film antennas by increasing the conductivity of thesurface. This is typically accomplished by increasing the thickness ortype of conductive material applied, or by placing relatively thicksheets of non-transparent highly conductive material on the antenna. Indoing so, the antennas become non-transparent.

U.S. Pat. No. 8,941,095 to Song et al., entitled “Methods forintegrating and forming optically transparent devices on surfaces,”describes an ideal thin-film antenna as having regions of perfectelectrical conductivity and regions of glass, which is an insulatingdielectric. Song et al. propose using films of silver nanowire orgraphene or other conductive materials such as ITO, that all givecompromised performance. U.S. Pat. No. 9,504,164 to Ramakrishnan et al.,entitled “Manufacturing of high resolution conductive patterns usingorganometallic ink and banded anilox rolls,” describes a method ofmaking a touch sensor which includes flexographically printing a patternof thin lines on a region of a substrate, and then plating the patternto create a pattern of microwires on the region of the substrate thatexhibits high conductivity and high transparency. Areas that are notpatterned and plated remain in an insulative state. The method describedby Ramakrishnan et al. can be adapted to make a thin-film antenna,however the viewing conditions for a touch screen application is verydifferent from that of a transparent antenna.

The touch screens of Ramakrishnan et al. are applied onto a digitaldisplay for applications that require touch input, such as cell phonesand computers. In these applications, the touch screens have a veryuniform pattern throughout the functional area; the touch screens areback lit (typically by LED displays); and the viewing conditions arenormally in relatively low intensity indoor lighting environments.

In contrast, window mounted thin-film antennas are typically used inbrightly lit viewing conditions (e.g., outdoor sunlight), the antennapattern is typically much smaller than the entire glass surface to whichit is affixed, the antenna can be viewed from both sides, withtransmissive and reflective visibility requirements, and theconductivity requirement for the conductive regions is typically muchhigher than for a capacitive touch screen.

There remains a need for improved thin-film conducting antennas that canbe incorporated into transparent surfaces without compromising antennaperformance or unnecessarily obstructing the optical view through suchsurfaces and that are undetectable to a human observer.

SUMMARY OF THE INVENTION

The present invention represents a transparent antenna, including:

a non-opaque substrate;

a conductive material disposed on a surface of the substrate in one ormore conductive regions, wherein a geometry of the conductive regionsdefines an antenna pattern;

a non-conductive material disposed on the surface of the substrate in afill pattern including one or more non-conductive regions, wherein thefill pattern is an inverse of the antenna pattern within a definedregion of interest; and

wherein an average optical transparency in the conductive regions is atleast 50%, wherein an average optical transparency in the non-conductiveregions is at least 50%, and wherein the average optical transparency inthe conductive regions differs from the average optical transparency inthe non-conductive regions by no more than 10%.

This invention has the advantage that an antenna can be provided on atransparent surface that is visually undetectable. The antenna is formedusing a pattern of micro-wires having a low visibility. The visibilityof the antenna pattern is further masked by surrounding it by a fillpattern of a non-conductive material which has matching opticalcharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a flexographic printing system forroll-to-roll printing on both sides of a substrate;

FIG. 2 is a schematic side view of a roll-to-roll electroless platingsystem;

FIG. 3 is a plan view of a planar antenna geometry;

FIG. 4A-4C illustrate different patterns appropriate for use inconductive and non-conductive regions in embodiments of the presentinvention;

FIGS. 5A-5C illustrate the formation of a transparent antenna includinga conductive antenna pattern and a complementary non-conductive fillpattern according to an exemplary embodiment;

FIG. 6A-6C illustrate an alternate embodiment of a transparent antennaincluding a blurred outer edge in a transition region;

FIG. 7 illustrates transparent antennas incorporated into windows of anautomobile;

FIG. 8 illustrates a transparent antenna incorporated into a buildingwindow; and

FIG. 9 illustrates a transparent antenna incorporated into a helmetvisor.

It is to be understood that the attached drawings are for purposes ofillustrating the concepts of the invention and may not be to scale.Identical reference numerals have been used, where possible, todesignate identical features that are common to the figures.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elementsforming part of, or cooperating more directly with, an apparatus inaccordance with the present invention. It is to be understood thatelements not specifically shown, labeled, or described can take variousforms well known to those skilled in the art. In the followingdescription and drawings, identical reference numerals have been used,where possible, to designate identical elements. It is to be understoodthat elements and components can be referred to in singular or pluralform, as appropriate, without limiting the scope of the invention.

The invention is inclusive of combinations of the embodiments describedherein. References to “a particular embodiment” and the like refer tofeatures that are present in at least one embodiment of the invention.Separate references to “an embodiment” or “particular embodiments” orthe like do not necessarily refer to the same embodiment or embodiments;however, such embodiments are not mutually exclusive, unless soindicated or as are readily apparent to one of skill in the art. Itshould be noted that, unless otherwise explicitly noted or required bycontext, the word “or” is used in this disclosure in a non-exclusivesense.

The example embodiments of the present invention are illustratedschematically and not to scale for the sake of clarity. One of ordinaryskill in the art will be able to readily determine the specific size andinterconnections of the elements of the example embodiments of thepresent invention.

References to upstream and downstream herein refer to direction of flow.Web media moves along a media path in a web advance direction fromupstream to downstream. Similarly, fluids flow through a fluid line in adirection from upstream to downstream. In some instances, a fluid canflow in an opposite direction from the web advance direction. Forclarification herein, upstream and downstream are meant to refer to theweb motion unless otherwise noted.

FIG. 1 is a schematic side view of a flexographic printing system 100that can be used in some embodiments of the invention for roll-to-rollprinting of a catalytic ink on both sides of a substrate 150 forsubsequent electroless plating. Substrate 150 is fed as a web fromsupply roll 102 to take-up roll 104 through flexographic printing system100. Substrate 150 has a first side 151 and a second side 152.

The flexographic printing system 100 includes two print modules 120 and140 that are configured to print on the first side 151 of substrate 150,as well as two print modules 110 and 130 that are configured to print onthe second side 152 of substrate 150. The web of substrate 150 travelsoverall in roll-to-roll direction 105 (left to right in the example ofFIG. 1). However, various rollers 106 and 107 are used to locally changethe direction of the web of substrate as needed for adjusting webtension, providing a buffer, and reversing the substrate 150 forprinting on an opposite side. In particular, note that in print module120, roller 107 serves to reverse the local direction of the web ofsubstrate 150 so that it is moving substantially in a right-to-leftdirection.

Each of the print modules 110, 120, 130, 140 includes some similarcomponents including a respective plate cylinder 111, 121, 131, 141, onwhich is mounted a respective flexographic printing plate 112, 122, 132,142, respectively. Each flexographic printing plate 112, 122, 132, 142has raised features 113 defining an image pattern to be printed on thesubstrate 150. Each print module 110, 120, 130, 140 also includes arespective impression cylinder 114, 124, 134, 144 that is configured toforce a side of the substrate 150 into contact with the correspondingflexographic printing plate 112, 122, 132, 142. Impression cylinders 124and 144 of print modules 120 and 140 (for printing on first side 151 ofsubstrate 150) rotate counter-clockwise in the view shown in FIG. 1,while impression cylinders 114 and 134 of print modules 110 and 130 (forprinting on second side 152 of substrate 150) rotate clockwise in thisview.

Each print module 110, 120, 130, 140 also includes a respective aniloxroller 115, 125, 135, 145 for providing ink to the correspondingflexographic printing plate 112, 122, 132, 142. As is well known in theprinting industry, an anilox roller is a hard cylinder, usuallyconstructed of a steel or aluminum core, having an outer surfacecontaining millions of very fine dimples, known as cells. Ink isprovided to the anilox roller by a tray or chambered reservoir (notshown). In some embodiments, some or all of the print modules 110, 120,130, 140 also include respective UV curing stations 116, 126, 136, 146for curing the printed ink on substrate 150.

FIG. 2 is a schematic side view of a roll-to-roll electroless platingsystem 200 disclosed in commonly-assigned, co-pending U.S. PatentApplication Publication 2016/0168713 entitled “Roll-to-roll electrolessplating system with liquid flow bearing,” by S. Reuter et al., which isincorporated herein by reference. The roll-to-roll electroless platingsystem 200 includes a tank 230 of plating solution 210. A web ofsubstrate 150 is fed by a web advance system along a web-transport pathin an in-track direction 205 from a supply roll 202 to a take-up roll204. The web of substrate 150 is a substrate upon which electrolessplating is to be performed. Drive roller 206 is positioned upstream ofthe plating solution 210 and drive roller 207 is positioned downstreamof the plating solution 210. Drive rollers 206 and 207 advance the webof substrate 150 from the supply roll 202 through the tank of platingsolution 210 to the take-up roll 204. Web-guiding rollers 208 are atleast partially submerged in the plating solution 210 in the tank 230and guide the web of substrate 150 along the web-transport path in thein-track direction 205.

As the web of substrate 150 is advanced through the plating solution 210in the tank 230, a metallic plating substance such as copper, silver,gold, nickel or palladium is electrolessly plated from the platingsolution 210 onto predetermined locations on one or both of a firstsurface 151 and a second surface 152 of the web of substrate 150. As aresult, the concentration of the metal or other components in theplating solution 210 in the tank 230 decreases and the plating solution210 needs to be refreshed. To refresh the plating solution 210, it isrecirculated by pump 240, and replenished plating solution 215 from areservoir 220 is added under the control of controller 242, which caninclude a valve (not shown). In the example shown in FIG. 2, platingsolution 210 is moved from tank 230 to pump 240 through a drain pipe 232and is returned from pump 240 to tank 230 through a return pipe 234. Inorder to remove particulates from plating solution 210, a filter 236 canbe included, typically downstream of the pump 240.

FIG. 3 shows an exemplary thin-film antenna 300 that includes anon-opaque substrate 150 (i.e., a substrate that is at least partiallytransparent) overlaid with a conductive planar antenna pattern 320.Preferably, the substrate has an optical transparency that is at least50% in a relevant wavelength range (e.g., the visible wavelength range).Examples of appropriate substrates would include plastic substrates(such polyester, polycarbonate or acrylic) or glasses (such as Corning®Willow® Glass). The thin-film antenna 300 can be configured to receiveor transmit signals in the frequency band relevant for a particularapplication (e.g., RF frequencies, microwave frequencies ormillimeter-wave frequencies). Methods for designing antenna patterns 320appropriate for different applications are well-known in the art.

The exemplary thin-film antenna 300 illustrated in FIG. 3 shows acompound multi-frequency RF antenna pattern that includes featuressimilar to those found in a slot antenna such as is shown in U.S. Pat.No. 6,911,952 to E. Sievenpiper, entitled “Crossed-slot antenna formobile satellite and terrestrial radio reception,” and an apertureantenna such as is shown in U.S. Pat. No. 7,233,296 to H. Song et al.,entitled “Transparent thin-film antenna.” The antenna pattern 320includes a center conductor signal strip (conductive region 365) andcoplanar ground regions (conductive region 360), together with an innernon-conductive region 380 and outer non-conductive region 381.Preferably the conductive regions 360, 365 have a resistance of no morethan 1 ohm/square.

In a preferred embodiment, the conductive regions 360, 365 of thethin-film antenna 300 are fabricated by using a printing press, such asthe flexographic printing system 100 of FIG. 1, to print a pattern ofcatalytic ink, and then using a roll-to-roll electroless plating system200 (FIG. 2) to plate a layer of metal over the catalytic ink. However,it will be clear to one skilled in the art that the pattern ofconductive regions 360, 365 can be formed using a variety of methodsknown in the art. For example, a gravure printing press can be usedinstead of the flexographic printing system 100. In another embodiment,the thin-film antenna 300 can be formed using an imprint and filltechnique such as that disclosed in commonly-assigned U.S. Pat. No.8,865,292 to D. Trauernicht et al., entitled “Micro-channel structurefor micro-wires,” which is incorporated herein by reference.

In an exemplary configuration, the conductive regions 360, 365 consistof microwire meshes formed using the electroless plating methoddescribed previously relative to FIGS. 1-2 to deposit thin conductivemicrowires with sufficient density to achieve the required conductivityand with sufficient spacing between the microwires to achieve therequired transparency. FIG. 4A shows an exemplary microwire mesh pattern410 that can be used in the conductive regions 360, 365. This meshpattern 410 includes a pattern of interconnected microwires 412 and ispreferred for isotropic electrical conductivity. The halftone patterns430, 431 shown in FIG. 4B are not generally useful for electricalconductivity, but can be used to aid in masking the thin-film antenna300 to make it more difficult to see. Similarly, FIG. 4C illustrates ahalftone pattern 440 incorporating a density gradient.

In some embodiments, a protective layer of transparent material can bedisposed over the conductive regions 360, 365 and the non-conductiveregions 380, 381 on the surface of the substrate 150 to protect thethin-film antenna 300 from being damaged. For example, a layer ofprotective material can be laminated over the surface of the substrate.

Typically, the thin-film antenna 300 is formed on a flexible transparentsubstrate 150. In some configurations, the substrate with the thin-filmantenna 300 can then be laminated onto the surface of a window (e.g.,and automobile window, a building window or a helmet visor). The windowcan be made of a variety of materials such as glass, polycarbonate oracrylic. Preferably, the surface having the thin-film antenna 300 canface the window to protect it from physical damage. In some cases, thesubstrate with the thin-film antenna 300 can be laminated between twopieces of glass. In some arrangements, a portion of the thin-filmantenna 300 that includes contact points can extend beyond the edges ofthe glass so that the thin-film antenna 300 can be connected toappropriate electrical circuitry.

Window mounted thin-film antennas are difficult to make completelyinvisible (while maintaining sufficient wire density) because they areoften viewed in brightly lit viewing conditions (e.g., outdoorsunlight), the antenna pattern is typically much smaller than the entireglass surface to which it is affixed, and the antenna can be viewed fromboth sides, with both transmissive and reflective invisibilityrequirements. Thus, several methods for masking the visibility of thethin-film antennas (i.e., making them more difficult to detect visually)will be described.

The ink that is used in the flexographic printing system 100 shown inFIG. 1 remains on the substrate 150 even after electroless plating. Theink contains metal particles, such as silver nanoparticles, that act asnucleation sites for the electroless plating process. Preferably, theink can also contain pigment particles that cause the printed inkpattern to have a matte neutral color. The printed ink pattern willstill be visible when viewing the antenna from the first side 151 of thesubstrate 150 so that it will appear to have a matte neutral color. Insome configurations, after plating the ink with a metal such as copper,the substrate 150 with the microwires can be put through a second bathto apply a darkening agent. In an exemplary configuration, palladium isused as a darkening agent. This darkening agent covers the second sideof the plated metal microwires as well as the edges of the microwires asthey are also exposed to the bath with the darkening agent. Both thedarkening agent and the ink with the pigment particles that cover themetal wires have the beneficial effect of creating a neutral color andreducing reflection and glint off the metallic surfaces of themicrowires when they are viewed from the second side 152 of thesubstrate 150.

The flexographic printing system 100 (FIG. 1) has the capability toprint a plurality of patterns on the substrate 150 in very goodregister. In an exemplary embodiment, one of the flexographic printingplates 112 is used to print the antenna pattern 320, and another of theflexographic printing plates 132 is used to print a complementary image302 which includes an inverse pattern 385 as illustrated in FIGS. 5A-5C.The complementary image 302 is printed using a non-catalytic inkcontaining a pigment but no metallic nanoparticles. The non-catalyticink is non-conductive and does not serve as a catalyst for theelectroless plating process. In this way, the complementary image 302 isinsulating so that it does not degrade the performance of the thin-filmantenna. The required close alignment of the inverse pattern 385 withthe antenna pattern 320 is enabled by the precision alignmentcapabilities of the flexographic printing system 100.

The inverse pattern 385 is an inverse of the antenna pattern 320 withina defined region of interest 315, and shares one or more commonboundaries with the antenna pattern 320. Within the region of interest315, a fill pattern 387 is printed in the areas of the complementaryimage 302 corresponding to the non-conductive regions 380, 381 of theantenna patter 320, and no fill pattern 387 is printed in thecomplementary image 302 in the areas corresponding to the conductiveregions 360, 365 of the antenna pattern 320. The inverse pattern 385 canalso be called a “complementary pattern” or a “fill pattern” in thesense that it is complementary to the antenna pattern 320 and fills theopen areas within and around the antenna pattern 320. In an exemplaryconfiguration, both the antenna pattern 320 and the inverse pattern 385are printed on the same side of the substrate 150, however this is not arequirement.

In some configurations, the fill regions 387 of the inverse pattern 385can be printed using a pattern of lines having a pattern geometry whichmatches the pattern of interconnected microwires in the conductiveregions 360, 365 of the antenna pattern 320. For example, if theconductive regions 360, 365 are formed using the mesh pattern 410 ofFIG. 4A, the fill regions 387 can be formed using a pattern ofnon-conductive lines arranged in the same mesh pattern 410. Within thecontext of the present disclosure the pattern geometry of the pattern oflines in the fill regions 387 is said to match the pattern of microwiresin the conductive regions 360, 365 if they have the same line spacingand line angles. (They do not necessarily have the same line width.) Inother configurations, the fill regions 387 can be printed using othertypes of patterns such as halftone patterns 430, 431 (FIG. 4C) oruniform density patterns (not shown).

The apparent density and color of the fill pattern 387 in thecomplementary image 302 is preferably chosen to closely match that ofthe metal-plated conductive regions 360, 365 (i.e., the radiativeportions) in the thin-film antenna 300 so that when the images areoverlaid with each other to form a composite antenna 304 the result is avisually uniform image appearance as shown in FIG. 5C so that theantenna is more difficult to detect and preferably visuallyundetectable. Within the context of the present disclosure, “visuallyundetectable” means that the structure of the thin-film antenna 300 isnot readily detectable with the unaided eye for a typical human observerviewing the composite antenna 304 at a specified viewing distance. Saidanother way, the thin-film antenna 300 is substantially visuallyindistinguishable from the complementary image 302. The relevant viewingdistance may be application dependent. For example, for cases where thethin-film antenna 300 is integrated into an automobile windshield, therelevant viewing distance would be the distance from the normal positionof the driver's head to the position of the thin-film antenna 300 on thewindshield.

The density (or equivalently the average optical transparency) of thefill pattern 387 can be controlled by adjusting the linewidth or linespacing in the mesh pattern 410 or the halftone dot size of the halftonepattern 430, 431. The color of the fill pattern 387 can be controlled bythe composition of the non-catalytic ink that is used to print thecomplementary image. Generally, it is desirable if the average opticaltransparency of the fill pattern 387 in the non-conductive regions 380,381 differs from the average optical transparence of the conductiveregions 360, 365 of the thin-film antenna 300 by no more than 10%. Morepreferably the average optical transparencies differ by 3% or less.Preferably, the average optical reflectance of the fill pattern 387 andthe conductive regions 360, 365 are also controlled such that theydiffer by no more than 10%, and more preferably by nor more than 50%.

The color difference between the fill pattern 387 in the non-conductiveregions 380, 381 and the conductive regions 360, 365 of the thin-filmantenna 300 can be characterized using any metric known in the colormeasurement art, such as the well-known CIE ΔE* metric. Preferably thecolor difference should be no more than 10 ΔE*, and more preferably is 3ΔE* or less.

In a preferred configuration, the resulting composite antenna 304 issubstantially transparent so that it can be applied on a window (e.g.,an automobile window) without significantly affecting the ability of anobserver to look through the window. In many applications, it isdesirable that the average optical transparency of both the fill pattern387 in the non-conductive regions 380, 381 and the conductive regions360, 365 of the thin-film antenna 300 be at least 50%, and morepreferably at least 80%.

Depending on the average optical transparency of the fill pattern 387 inthe non-conductive regions 380, 381 and the conductive regions 360, 365of the thin-film antenna 300, the edges of the composite antenna 304 maybe visually detectable even if the thin-film antenna 300 is visuallyindistinguishable from the fill pattern 387. FIGS. 6A-6C illustrate analternate confirmation where a composite antenna 308 is formed having atransition region 310 to reduce the visibility of the edges of thecomposite antenna 308. The composite antenna 308 is formed by combiningthe same antenna pattern 320 that was shown in FIG. 5A with acomplementary image 306 including a complementary pattern 386 with ablurred outer edge in a transition region 310. The transition region 310has an outer boundary 312 and an inner boundary corresponding to theother boundary of the region of interest 315. The transition region 310provides a smooth transition between the average optical transparency ofthe fill pattern 387 and the higher optical transparency of thesubstrate 150. As is well-known to those skilled in the art, the humanvisual system is more sensitive to detecting sharp edges than it is todetecting gradual gradients. As a result, the use of a transition region310 can substantially mask, or even eliminate, the visibility of theedges of the composite antenna 307. In some configurations, thetransition region 310 can be formed using a gradient halftone pattern440 such as that illustrated in FIG. 4D.

In some applications, the composite antenna 304 (FIG. 5C) can be placedin a portion of a window where a high level of optical transparency isnot critical, such as in the top or bottom portion of an automobilewindshield. These portions of the windshield are often tinted so thatthey have a transparency of less than 50%. In such cases, the opticaltransparency and color of the composite antenna 304 can be controlled tosubstantially match the transparency of the tinted region (e.g., towithin 10%), or can actually serve to provide the tinting. In this case,even though the overall density of the composite antenna 304 may bevisible to an observer, the antenna pattern 320 will be visuallyindistinguishable from the fill pattern 387 and the window tint so thatthe antenna pattern 320 will be visually undetectable.

FIG. 7 shows an automobile 500 where a shade band, shown as a tintedregion 510, is provided at the top of the windshield 505. Two compositeantennas 304, such as those described with respect to FIG. 5C, areprovided in the tinted region 510. The average optical transparency andcolor of the composite antenna 304 (i.e., the average opticaltransparency and color of the metal-plated conductive regions 360, 365in the thin-film antenna 300 and the fill pattern 387 in thecomplementary image 302 (see FIGS. 5A-5B)) are controlled to closelymatch each other and to match that of the tinted region 510 such thatthe composite antenna 304 is visually indistinguishable to an un-aidedobserver at a normal viewing distance. In some embodiments, the regionof interest 315 for the composite antenna 304 can correspond to theentire area of the tinted region 510 such that the composite antenna 304can be used to provide the tinting for the tinted region 510 without theneed for additional tinting features. In this case, the average opticaltransparency and color of the composite antenna 304 can be selected toprovide the desire density and color of the tinted region 510.

In some applications, it is useful to provide a variety of antennas inthe windows of the automobile 500 to serve various purposes (e.g., AMradio, FM radio, GPS, cell phone, WiFi, etc.). In the illustratedconfiguration, in addition to the composite antennas 304 provided in thetinted region 510 of the windshield 505, an additional composite antenna308 is provided in a lower corner of the windshield 505, and twoadditional composite antennas 308 are provided in the rear window 515.In this case, the additional composite antennas 308 include transitionregions 310 as shown in FIG. 6C to reduce the visibility of the edges ofthe antenna regions.

It will be obvious to one skilled in the art that the transparentcomposite antennas 304 of the present invention can be used for a widevariety of other applications. For example, they can be incorporatedinto other types of windows such as building windows and helmet visors(e.g., motorcycle helmets or military helmets), or into any other typeof transparent or semi-transparent surface (e.g., tinted windows orvisors). They can also be overlaid onto an opaque surface (e.g., a wall)such that they are substantially undetectable to an observer. FIG. 8shows an example of a composite antenna 304 incorporated into a window610 of a building 600, and FIG. 9 shows an example of a compositeantenna 304 incorporated into a visor 630 of a helmet 620. In both ofthese cases, the window 610 or the visor 630 may include a tint, inwhich case the transparency and color of the composite antenna 304 ispreferably controlled to match the tint or to produce the desired tint.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   100 flexographic printing system-   102 supply roll-   104 take-up roll-   105 roll-to-roll direction-   106 roller-   107 roller-   110 print module-   111 plate cylinder-   112 flexographic printing plate-   113 raised features-   114 impression cylinder-   115 anilox roller-   116 UV curing station-   120 print module-   121 plate cylinder-   122 flexographic printing plate-   124 impression cylinder-   125 anilox roller-   126 UV curing station-   130 print module-   131 plate cylinder-   132 flexographic printing plate-   134 impression cylinder-   135 anilox roller-   136 UV curing station-   140 print module-   141 plate cylinder-   142 flexographic printing plate-   144 impression cylinder-   145 anilox roller-   146 UV curing station-   150 substrate-   151 first side-   152 second side-   200 roll-to-roll electroless plating system-   202 supply roll-   204 take-up roll-   205 in-track direction-   206 drive roller-   207 drive roller-   208 web-guiding roller-   210 plating solution-   215 replenished plating solution-   220 reservoir-   230 tank-   232 drain pipe-   234 return pipe-   236 filter-   240 pump-   242 controller-   300 thin-film antenna-   302 complementary image-   304 composite antenna-   306 complementary image-   308 composite antenna-   310 transition region-   312 outer boundary-   315 region of interest-   320 antenna pattern-   360 conductive region-   365 conductive region-   380 non-conductive region-   381 non-conductive region-   385 inverse pattern-   386 complementary pattern-   387 fill pattern-   410 mesh pattern-   412 microwire-   430 halftone pattern-   431 halftone pattern-   440 halftone pattern-   500 automobile-   505 windshield-   510 tinted region-   515 rear window-   600 building-   610 window-   620 helmet-   630 visor

1. A transparent antenna, comprising: a non-opaque substrate; aconductive material disposed on a surface of the substrate in one ormore conductive regions, wherein a geometry of the conductive regionsdefines an antenna pattern; a non-conductive material disposed on thesurface of the substrate in a fill pattern including one or morenon-conductive regions, wherein the fill pattern is an inverse of theantenna pattern within a defined region of interest; and wherein anaverage optical transparency in the conductive regions is at least 50%,wherein an average optical transparency in the non-conductive regions isat least 50%, and wherein the average optical transparency in theconductive regions differs from the average optical transparency in thenon-conductive regions by no more than 10%.
 2. The transparent antennaof claim 1, wherein the non-conductive region shares one or moreboundaries with the conductive region.
 3. The transparent antenna ofclaim 1, wherein the conductive material in the conductive regionincludes a pattern of interconnected microwires.
 4. The transparentantenna of claim 3, wherein the pattern of interconnected microwires isa mesh pattern.
 5. The transparent antenna of claim 3, wherein thenon-conductive material in the non-conductive region includes a patternof lines having a pattern geometry which matches that of the pattern ofinterconnected microwires in the conductive region.
 6. The transparentantenna of claim 1, wherein the non-conductive material in thenon-conductive region includes a pattern of lines.
 7. The transparentantenna of claim 6, wherein the pattern of lines is a mesh pattern. 8.The transparent antenna of claim 1, wherein the non-conductive materialin the non-conductive region includes a pattern of halftone dots.
 9. Thetransparent antenna of claim 1, wherein the conductive material is ametal.
 10. The transparent antenna of claim 1, wherein thenon-conductive material is a non-conductive ink.
 11. The transparentantenna of claim 1, further including a protective layer of transparentmaterial disposed over the conductive material and the non-conductivematerial on the surface of the substrate.
 12. The transparent antenna ofclaim 1, wherein the substrate is polyester, glass, polycarbonate oracrylic.
 13. The transparent antenna of claim 1, wherein the antennapattern is visually indistinguishable from the fill pattern to a humanobserver.
 14. The transparent antenna of claim 1, wherein thetransparent antenna is laminated onto a rigid window.
 15. Thetransparent antenna of claim 14, wherein the window is an automobilewindow, a building window or a helmet visor.
 16. The transparent antennaof claim 14, wherein the transparent antenna is positioned within atinted portion of the window.
 17. The transparent antenna of claim 16,wherein the average optical transparency in the conductive region andthe average optical transparency in the non-conductive region match anaverage optical transparency of the tinted portion of the window towithin 10%.
 18. The transparent antenna of claim 1, wherein thetransparent antenna is configured to operate at one of RF, microwave andmillimeter-wave frequencies.
 19. The transparent antenna of claim 1,wherein the conductive region has a resistance of no more than 1ohm/square.
 20. The transparent antenna of claim 1, wherein the averageoptical transparency in the conductive region is at least 80%, andwherein the average optical transparency in the non-conductive region isat least 80%.
 21. The transparent antenna of claim 1, wherein theaverage optical transparency in the conductive region differs from theaverage optical transparency in the non-conductive region by no morethan 3%.
 22. The transparent antenna of claim 1, further including atransition region adjacent to the region of interest, wherein thetransition region has an outer boundary and an inner boundary, the innerboundary corresponding to an outer boundary of the region of interest,wherein the non-conductive material is disposed on the surface of thesubstrate in the transition region, and wherein an average opticaltransparency in the transition region transitions from a first averageoptical transparency at the inner boundary to a higher second averageoptical transparency at the outer boundary.